{"id":"CVE-2024-42305","summary":"ext4: check dot and dotdot of dx_root before making dir indexed","details":"In the Linux kernel, the following vulnerability has been resolved:\n\next4: check dot and dotdot of dx_root before making dir indexed\n\nSyzbot reports a issue as follows:\n============================================\nBUG: unable to handle page fault for address: ffffed11022e24fe\nPGD 23ffee067 P4D 23ffee067 PUD 0\nOops: Oops: 0000 [#1] PREEMPT SMP KASAN PTI\nCPU: 0 PID: 5079 Comm: syz-executor306 Not tainted 6.10.0-rc5-g55027e689933 #0\nCall Trace:\n \u003cTASK\u003e\n make_indexed_dir+0xdaf/0x13c0 fs/ext4/namei.c:2341\n ext4_add_entry+0x222a/0x25d0 fs/ext4/namei.c:2451\n ext4_rename fs/ext4/namei.c:3936 [inline]\n ext4_rename2+0x26e5/0x4370 fs/ext4/namei.c:4214\n[...]\n============================================\n\nThe immediate cause of this problem is that there is only one valid dentry\nfor the block to be split during do_split, so split==0 results in out of\nbounds accesses to the map triggering the issue.\n\n    do_split\n      unsigned split\n      dx_make_map\n       count = 1\n      split = count/2 = 0;\n      continued = hash2 == map[split - 1].hash;\n       ---\u003e map[4294967295]\n\nThe maximum length of a filename is 255 and the minimum block size is 1024,\nso it is always guaranteed that the number of entries is greater than or\nequal to 2 when do_split() is called.\n\nBut syzbot's crafted image has no dot and dotdot in dir, and the dentry\ndistribution in dirblock is as follows:\n\n  bus     dentry1          hole           dentry2           free\n|xx--|xx-------------|...............|xx-------------|...............|\n0   12 (8+248)=256  268     256     524 (8+256)=264 788     236     1024\n\nSo when renaming dentry1 increases its name_len length by 1, neither hole\nnor free is sufficient to hold the new dentry, and make_indexed_dir() is\ncalled.\n\nIn make_indexed_dir() it is assumed that the first two entries of the\ndirblock must be dot and dotdot, so bus and dentry1 are left in dx_root\nbecause they are treated as dot and dotdot, and only dentry2 is moved\nto the new leaf block. That's why count is equal to 1.\n\nTherefore add the ext4_check_dx_root() helper function to add more sanity\nchecks to dot and dotdot before starting the conversion to avoid the above\nissue.","modified":"2026-03-20T12:38:46.626099Z","published":"2024-08-17T09:09:11.296Z","related":["MGASA-2024-0309","MGASA-2024-0310","SUSE-SU-2024:3551-1","SUSE-SU-2024:3559-1","SUSE-SU-2024:3561-1","SUSE-SU-2024:3564-1","SUSE-SU-2024:3566-1","SUSE-SU-2024:3569-1","SUSE-SU-2024:3587-1","SUSE-SU-2024:3591-1","SUSE-SU-2024:3592-1","SUSE-SU-2025:20073-1","SUSE-SU-2025:20077-1"],"database_specific":{"cna_assigner":"Linux","osv_generated_from":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2024/42xxx/CVE-2024-42305.json"},"references":[{"type":"WEB","url":"https://git.kernel.org/stable/c/19e13b4d7f0303186fcc891aba8d0de7c8fdbda8"},{"type":"WEB","url":"https://git.kernel.org/stable/c/42d420517072028fb0eb852c358056b7717ba5aa"},{"type":"WEB","url":"https://git.kernel.org/stable/c/50ea741def587a64e08879ce6c6a30131f7111e7"},{"type":"WEB","url":"https://git.kernel.org/stable/c/8afe06ed3be7a874b3cd82ef5f8959aca8d6429a"},{"type":"WEB","url":"https://git.kernel.org/stable/c/9d241b7a39af192d1bb422714a458982c7cc67a2"},{"type":"WEB","url":"https://git.kernel.org/stable/c/abb411ac991810c0bcbe51c2e76d2502bf611b5c"},{"type":"WEB","url":"https://git.kernel.org/stable/c/b80575ffa98b5bb3a5d4d392bfe4c2e03e9557db"},{"type":"WEB","url":"https://git.kernel.org/stable/c/cdd345321699042ece4a9d2e70754d2397d378c5"},{"type":"WEB","url":"https://lists.debian.org/debian-lts-announce/2024/10/msg00003.html"},{"type":"WEB","url":"https://lists.debian.org/debian-lts-announce/2025/01/msg00001.html"},{"type":"ADVISORY","url":"https://github.com/CVEProject/cvelistV5/tree/main/cves/2024/42xxx/CVE-2024-42305.json"},{"type":"ADVISORY","url":"https://nvd.nist.gov/vuln/detail/CVE-2024-42305"},{"type":"PACKAGE","url":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git"}],"affected":[{"ranges":[{"type":"GIT","repo":"https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git","events":[{"introduced":"ac27a0ec112a089f1a5102bc8dffc79c8c815571"},{"fixed":"b80575ffa98b5bb3a5d4d392bfe4c2e03e9557db"},{"fixed":"19e13b4d7f0303186fcc891aba8d0de7c8fdbda8"},{"fixed":"42d420517072028fb0eb852c358056b7717ba5aa"},{"fixed":"8afe06ed3be7a874b3cd82ef5f8959aca8d6429a"},{"fixed":"abb411ac991810c0bcbe51c2e76d2502bf611b5c"},{"fixed":"9d241b7a39af192d1bb422714a458982c7cc67a2"},{"fixed":"cdd345321699042ece4a9d2e70754d2397d378c5"},{"fixed":"50ea741def587a64e08879ce6c6a30131f7111e7"}]}],"database_specific":{"source":"https://storage.googleapis.com/osv-test-cve-osv-conversion/osv-output/CVE-2024-42305.json"}}],"schema_version":"1.7.5"}